This invention relates to ink jet heads having piezoelectric transducers for use in ink jet systems and, more particularly, to a new and improved ink jet head having a thin-film piezoelectric transducer.
In certain ink jet systems, the ink jet head contains ink chambers in which one wall or wall portion is provided by a plate-like piezoelectric element which moves laterally so as to expand or contract the volume of the chamber in response to electrical signals. Heretofore, such plate-like piezoelectric transducers have consisted of a continuous sheet of piezoelectric material forming the transducers for a series of adjacent ink jet chambers, as described, for example, in the Fischbeck et al. U.S. Pat. No. 4,584,590, or of individual plate-like piezoelectric elements disposed adjacent to each ink jet chamber, as disclosed, for example, in the Cruz-Uribe et al. U.S. Pat. No. 4,680,595. Moreover, as described in the Cruz-Uribe et al. patent, the individual transducers may, for example, be formed by etching to remove material from a single continuous sheet of piezoelectric material, leaving separate discrete transducers. Such conventional sheet-form piezoelectric materials are made, for example, by shaping green material into sheet form and firing, and they have a minimum thickness of about 3-5 mils (75-125 microns).
Because the extent of bending of a piezoelectric sheet material for a given applied voltage application is inversely proportional to the thickness of the sheet, the use of transducers having a minimum thickness of about 5 mils (125 microns) requires an ink chamber with a relatively large piezoelectric wall area in order to eject an ink drop of specific size, such as 80 picoliters. As a result of the large chamber wall area requirement, correspondingly large chamber size and orifice spacing, as well as ink jet head size, are required.
Sheet piezoelectric materials have further innate disadvantages in manufacturability. The materials tend to be fragile, which makes processing expensive. In addition, the sheet material must be bonded to at least one other part, which is generally a demanding process.